EP0203622A2 - Débitmètre thermique de masse et régulateur - Google Patents

Débitmètre thermique de masse et régulateur Download PDF

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Publication number
EP0203622A2
EP0203622A2 EP19860200194 EP86200194A EP0203622A2 EP 0203622 A2 EP0203622 A2 EP 0203622A2 EP 19860200194 EP19860200194 EP 19860200194 EP 86200194 A EP86200194 A EP 86200194A EP 0203622 A2 EP0203622 A2 EP 0203622A2
Authority
EP
European Patent Office
Prior art keywords
flow
gas
sensor
flowmeter
stagnant
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP19860200194
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German (de)
English (en)
Other versions
EP0203622B1 (fr
EP0203622A3 (en
Inventor
Wayne G. Renken
Dan B. Lemay
Richard M. Takahashi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Unit Instruments Inc
Original Assignee
Unit Instruments Inc
Innovus
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
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Publication of EP0203622A2 publication Critical patent/EP0203622A2/fr
Publication of EP0203622A3 publication Critical patent/EP0203622A3/en
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Publication of EP0203622B1 publication Critical patent/EP0203622B1/fr
Anticipated expiration legal-status Critical
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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/696—Circuits therefor, e.g. constant-current flow meters
    • G01F1/698—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6842—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow with means for influencing the fluid flow
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6845—Micromachined devices
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D7/00—Control of flow
    • G05D7/06—Control of flow characterised by the use of electric means
    • G05D7/0617—Control of flow characterised by the use of electric means specially adapted for fluid materials
    • G05D7/0629—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means
    • G05D7/0635—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means by action on throttling means
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/7722—Line condition change responsive valves
    • Y10T137/7758—Pilot or servo controlled
    • Y10T137/7759—Responsive to change in rate of fluid flow

Definitions

  • This invention relates to a thermal mass flowmeter and controller which includes sensors for measuring the mass flow rate of liquid or gaseous fluids, electromagnetic control valves, associated amplifiers, and bridge and signal conditioning circuits. It further relates to the utilization of semiconductor type materials to make extremely small and accurate flowmeters for measuring and controlling the flow of semiconductor processing gases, medical anesthetic gases, and gases used for analytic instruments.
  • U.S. Patent 4,478,076 shows a flow sensor consisting of a pair of heat sensors disposed on opposite sides of a heater.
  • the sensors and heaters are fabricated by depositing resistive material on a thin film of silicon nitride previously deposited on a silicon substrate. After patterning the resistor it may be encapsulated with a suitable thermal insulator such as silicon nitride. An air space etched out underneath the sensor elements allows air flow past the top and bottom of the sensors and heater.
  • U.S. Patent 4,471,647 describes in context of a gas chromatographic assembly, a thermal detector in which the gas being thermally measured passes through apertures in a silicon dioxide membrane containing sensor and heater elements.
  • the membrane - sensor structure is supported by a silicon substrate in which an aperture is etched to thermally isolate the membrane, provide perimeter support, and allow gases to pass through the substrate.
  • U.S. Patent 3,931,736 shows an improvement over fluid flow sensors which are positioned on the exterior surface of a conduit.
  • the improvement entails placing -a-thin imperforate membrane functioning as one wall of an active flow channel and a dead flow channel, the latter to obtain reference readings under conditions of substantially no fluid flow.
  • Sensors are placed on the surface of the membrane away from the channels so that the sensors are not in direct contact with the fluid.
  • the bottom surface of the membrane is in contact with the fluid and the sensor chips are thermally coupled to the membrane.
  • U.S. Patent 4,343,768 describes a catalytic gas detector formed from a self-heated temperature sensor deposited on a thin dielectric film supported by a substrate. The substrate is etched under the sensor region to form a physical bridge which is thermally isolated. Catalytic films are deposited on the heater-sensor to promote chemical reactions. The sensor measures heat generated by the reaction.
  • the above designs can be used to measure the mass flow rate of fluids passing parallel to and near the substrate surfaces. They have limited inherent accuracy because the sensor elements may not be placed at a location within the flow conduit where the local fluid velocity is representative of the total flow, and the substrate placement in the flow conduit may introduce turbulence - further decreasing measurement accuracy.
  • the present invention simplifes and improves the performance of mass flow meters. It enables highly accurate flow measurement utilizing an integral, controlled geometry flow conduit, and accurate placement of the sensor structures within the conduit. Flow velocities are limited, providing laminar flow within the conduit and above and below the sensor structures. High measurement accuracy - better than 99% - is achieved, with good signal levels - (10 to 40 millivolts). Very low measurement temperatures - typically 25°C rise above ambient enables measurements of reactive fluids with low decomposition temperatures. Low-mass sensor structures enable very fast response times - typically below 2 milliseconds. A high thermal conductivity cover substrate providing the upper portion of the flow conduit, protects the sensor elements from external radiation - a source of measurement error.
  • the cover substrate maintains uniform heat transfer from the sensor elements, limits gas convection at zero flow velocity, provides an accurate and stable zero flow signal, and eliminates offsets in the zero-flow signal when the sensor's position is shifted with respect to gravity.
  • Self heated flow sensors are supported on silicon oxynitride webs within flow channels and also within separate blocked, zero-flow, stagnant gas channels.
  • the reference signal derived from the stagnant gas blocked channel provides an accurate zero flow signal which improves the flowmeter accuracy.
  • a wall temperature sensor is formed on the silicon sensor substrate adjacent to the wall of the flow channel(s) to provide a measurement of local temperature and an accurate indication of the inlet gas temperature to the flow sensor.
  • the signal derived by comparing the stagnant gas sensor to the wall temperature sensor provides a measurement of gas properties affecting flow sensor sensitivity.
  • the amplified difference signal is used to control a bridge excitation current. Feedback means is used to regulate the temperature rise of the stagnant gas sensor above ambient, thereby tending to provide more constant gain.
  • a gas such as helium has high thermal conductivity and needs more excitation power to maintain the sensor's temperature rise, and thus signal strength.
  • the flow sensor versus the stagnant gas sensor provides a flow signal which is always null at zero flow by symmetry. Because of the variable bridge excitation current provided, the circuit has a gain which is at least partially compensates for gas dependent properties and their effect on sensitivity. Further correction of gain, linearity, and zero stability can be made by:
  • Various bridge circuits are connected to the wall temperature sensor and with a fixed resistor ratio reference to provide a temperature signal for compensation of a flow signal.
  • the mass flowmeter of the invention is preferably manufactured utilizing a channel layout with double planes of symmetry and in which redundant flow and stagnant flow sensor elements and conduits are provided to increase the yield of elements meeting desired specifications.
  • the above mass flowmeter is integrated into a mass flow controller.
  • the controller uses the above flow sensor which is a micromachined silicon sensor substrate assembly installed with an integral laminar flow element to increase the flow capacity.
  • the low-thermal-mass sensor elements respond to changes in mass flow in tenths of milliseconds while heating the gas to a maximum temperature of 25°C above ambient in the preferred embodiment, avoiding reactions in the gas and particulate formation.
  • the sensor assembly is close-coupled to a low mass, normally closed solenoid valve to achieve a response of less than 0.06 seconds to within 98% of flow set point with freedom from overshoot, flow surges, and oscillations.
  • the stainless steel plug-in housing has no external welds or threads exposed to the gas stream.
  • a low friction, spring-suspended valve armature is provided. High magnetic drive forces and a low mass armature enables stable, positive valve_control with minimum sensitivity to vibration.
  • the sensor elements are enclosed within the flow stream which provides high thermal isolation from the external environment, making the mass flow controller attitude independent and essentially free from calibration drift.
  • the valve consumes low power (below 2 watts) and has less than 1°C temperature rise in normal operation.
  • An alternative embodient of the invention utilizes a sensor on a web suspended within the flow channel near the inlet. It is used in place of the wall sensor to determine inlet gas temperature and to provide an ambient temperature reference for both the stagnant and flow sensors. Minimal power is utilized in the temperature measurement to reduce self heating and the resulting ambient temperature offset.
  • Another alternative embodiment of the invention utilizes diodes or transistors formed in thin silicon islands supported on a silicon oxynitride beam or bridge spanning the flow channel. Heat is produced by forward biasing the device junctions. Temperature is measured by sensing changes in the forward bias junction voltage drop which is a function of temperature.
  • Fig. 1 schematically shows an overall flowmeter and control system 10 comprising a single-crystal semiconductor sensor substrate lla forming one side of a gas flow channel or conduit 12 and blocked channel 13, and containing a thin film flow sensor R F and thin film stagnant gas sensor R S , respectively.
  • a thin film substrate temperature sensor R T is formed on said substrate near the two channels and measures the chip ambient temperature which is an indication of the temperature of the inlet gas flow shown by arrow 19.
  • a matching cover substrate 11b with etched grooves but without sensor elements is aligned and bonded to the sensor substrate to form stagnant and flow conduits 12, 13.
  • a bridge circuit 14 includes inputs from the sensors and has an output signal 18 (E out ) which in conjunction with a flow set point potentiometer 16 and amplifier 17 controls flow of gas through chip passage 12 and outwardly from the chip through conduit 15 to a gas-using apparatus (not shown) by movement of valve 15a in conduit 15.
  • R B , R C , R F1 ⁇ R S1' R S2' R T2 and R E are fixed resistors.
  • R F and R S are significantly influenced by the equilibrium between their self-heating (I 2 R) and their heat transfer to the gas.
  • Amplifier T 2 reproduces E S2 with no drain from I S .
  • R T2 /R S2 governs the magnitude of the regulated temperature rise of R S above R T .
  • An E B output signal is provided in both circuits Fig. 1 and Fig. 4 to allow remote monitoring of the bridge voltage.
  • Figs. 2 and 3 illustrate one embodiment of the sensor chip.
  • Thin film resistors 25, 31 and 34 are deposited on a dielectric film formed on the top surface 21 of a semiconductor substrate 20 of silicon or the like.
  • a flow channel groove 22 is formed by etching of the surface 21 (after suitable masking and other steps as is known in the semiconductor processing art and as described below) completely along a longitudinal extent of the substrate.
  • Apertures 33 are etched in the dielectric insulating membrane 26 to aid in the etching away of the underside of the web and to complete the fabrication of channel groove 22. The apertures also function to thermally isolate the web from the chip body.
  • Web 26 supports thin film resistor 25.
  • a stagnant gas channel_groove 23 is etched in the substrate surface extending only part-way into the substrate so that the channel groove is blocked by wall 24.
  • a membrane 30 supports thin film resistor 31 and contains apertures 33 which allow etchant access to the underside of the web.
  • a thin film temperature sensor 34 is formed in the same plane as sensors 25 and 31 on a portion 35 of surface 21, either between or next to one of the channel grooves 22 or 23 or at the gas inlet. Suitable leads in the form of metallization pathways 27, 28, 32 and 36 connect the sensor to bonding-contact pads and in turn to the bridge circuit.
  • the sensor is formed by the following process sequence:
  • Fig. 3 illustrates the preferred embodient of the chip sensor and cover assembly 11a and llb where a second semiconductor substrate 40 having flow channel groove(s) 42 and stagnant channel groove(s) 43 aligned with grooves 22 and 23, respectively, are bonded as at 44 to the first substrate 20.
  • the matching grooves thus form a flow conduit(s) and stagnant conduit(s).
  • the web or membrane 26 is shown bridging across the median between the grooves 22, 42 so that essentially laminar gas flow passes laterally over the top of the sensor membrane 26 and laterally under the bottom of that sensor membrane in the flow conduit.
  • Sensor 31 also bridges over a medial plane of the substrates but is essentially in a no-gas flow position due to the blocked channel 23, 43.
  • Body temperature sensor 34 is shown thermally bonded between facing surfaces 35, 35a of the two substrates.
  • Gas species estimation is useful for distinguishing between gases with moderate to significant differences in thermal condutivity when the gases are unknown, or estimating the composition of gas mixtures when the gases are known.
  • Valve control circuit gain need not be precise and should be a function of gas density. Equation (5) indicates that E B can provide that function. Since the primary function of the E B variation is flow sensor compensation, the secondary use of E B for gas species estimation and for valve gain control will be dependent upon the E B function optimized for the flow signal; i.e., after the circuit relationships in Fig. 1 have been optimized for the flow sensor, then the valve control circuit can be finalized for optimum use of that E B schedule for valve gain control. The E B signal is output to allow external monitoring of the signal which approximates gas thermal conductivity.
  • Fig. 6 graphically illustrates the temperature-time relationships of the three sensors during flowmeter operation.
  • Curve 50 represents the chip temperature sensed by resistor R T (Fig. 1) which slightly increases over time to a relatively constant value due to heat transfer to the chip walls from the flowing gas, heating input into the resistors R F , R S , and R T , and self-heating.
  • Curve 51 represents the temperature of the stagnant channel sensor R S which rises to a steady level above the chip temperature T T . Heating current energizing sensor R S is controlled so that a AT of approximately 25°C is maintained at steady state between R T and R S .
  • Curve 52 represents the temperature of flow sensor R F which is heated and utilized for flow (temperature) sensing.
  • Fig. 7 illustrates a preferred embodiment of the sensor substrate construction where a silicon chip 60 is fabricated having repetitive patterns thereon in two planes of symmetry.
  • one quadrant (A) of the overall substrate is detailed in Fig. 7 with the pattern being "flipped” and repeated to the right of axis 61 and the resultant double pattern "flipped” and repeated above axis 62.
  • the flow channel or groove 63b is a continuation of flow channel 63a formed in quadrant D.
  • Flow channel 63d is similarly a continuation of 63c. Entry of inlet gas is at the top edge of channels 63a and 63c.
  • the gas thus travels the length of channel 63a toward channel 63b and becomes laminar in flow. It passes the sensor in channel 63a (not shown) which is inoperative unless it is found that sensor 64 in channel 63 does not meet specification in which case the flow path would be reversed and the channel 63a sensor would be utilized in the bridge circuit. This increases yield from the chips which are fabricated.
  • This unused inlet sensor can be utilized in an alternate embodiment of the invention to measure inlet gas temperature in place of the wall sensor.
  • a second blocked channel 67a is opposite blocked channel 67b.
  • Blocked channel 67b has two sensors 65, 66 connected in series for a close resistance match with series flow sensors 64a and 64b.
  • a series of resistors 68 extend on a flat substrate surface in the same plane as resistors 64, 65 and 66 adjacent the edge of blocked channel 67b, but thermally coupled to the silicon chip to measure substrate temperature R T .
  • the pattern of the resistors 64a, 64b, 65, and 66 are identical to avoid resistance differences resulting from geometrical variations.
  • Suitable contact and bonding pads 69, 69a are provided on the outer edges of the chip for connection to the various sensors and by interconnecting metallization pathways 70 to the bridge circuit.
  • the set of sensors and channels in quadrant B to the right of axis 61 may be utilized to derive multiple signals to be compared for more accurate flow information or diagnosis of calibration shifts due to particulate obstructions.
  • the flow indication in either is utilized if both indicate similar flow.
  • a flow sensor indicating dissimilar and lower flow is disregarded indicating a closed, partially closed, or inoperative flow channel. This is fully explained in the related application, pages 9-10 and Fig. 2.
  • averaging several channel readings, e.g., four, and throwing out a reading which is at a prescribed level indicative of a blockage in flow in that channel, and then reaveraging the "good" remaining three channels is a function easily performed by a microprocessor and well within the ordinary skill in the concerned art.
  • a to D converter 24 receives flow signals from independent sensors from amplifier 23 and 25a, 25b and 25c.
  • Calibrator 28 contains within its PROM memory (page 11, lines 6-10) the output signal ratios of flow through each of channels 21 (Fig. 3 of the related application) measured in the uncontaminated state during manufacture and test. These ratios of one sensor output compared to another are intrinsic and are maintained over normal flow ranges if all channels remain free of contamination.
  • Controller 26 digitally averages flow sensor signals of all the channels resulting in a composite flow signal.
  • the controller 26 in the related application continuously compares the flow ratios among the flow sensor channels. If the ratios are not generally maintained to their original calibrated values (stored in PROM) the controller identifies the abnormal low-output from a channel output and excludes the channel(s) output from being averaged. This results in a composite flow signal excluding a low-output sensor. The controller then compares the composite flow signal to the requested set-point input and increases or decreases the valve drive signal to regulate flow through the downstream valve.
  • Fig. 8 shows a highly magnified view of the sensor 80, membrane, used in a stagnant (blocked) or flow channel.
  • Resistor sinuous patterns 73 with conductive pathways 74 leading to interconnecting pads are first formed on the silicon oxinitride film previously deposited on substrate 71. Certain portions of the silicon oxinitride film are then masked and etched to form large end apertures 76 and small slit-like apertures 77 to allow flow of etchant under the to-be-formed membrane 80.
  • the substrate is etched out under apertures 76 and 77 and in areas upstream and downstream of the sensor to form groove 79 they leave a membrane 80 integrally bridging or suspended across the groove.
  • Apertures 76 also function to thermally isolate the sensor from substrate 71. In use there is no purposeful flow of the gas under control through the apertures 76, 77. The gas flows parallel to the top and bottom surfaces of the membrane in essentially laminar flow as it traverses the facing grooves of the sensor and cover substrates making up the overall flow conduit e.g. 22, 42 in Fig. 3. The entire flow conduit is preferably passivated with silicon nitride.
  • Fig. 9 shows the preferred form of the invention utilizing an integral control valve arrangement.
  • the overall flow controller 81 comprises an outer housing 82 having an upper (the right side in Fig. 9) flow-sensor housing portion 82a, a mid-portion 82b housing a valve- actuating armature and a lower portion 82c housing working gas inlet 94 and outlet 98.
  • a valve seat 83 is inserted from the top of housing 82 and held within the interior of portion 82c adjacent outlet 98 and sealed by O-ring 87c.
  • Valve seat 83 contains a valve orifice 97 at its top.
  • An armature 84 which contains cylindrical flow passages 84a, is positioned above valve seat 83 with an open sinuous lever spring 84b therebetween, the outer periphery of the spring being seated on the valve seat top and the inner periphery against the armature bottom.
  • a second open sinuous lever spring 85a has an inner periphery seating on the top of the armature.
  • An annular pole piece 86 is inserted on top of spring 85a with its bottom contacting the outer periphery of spring 85a. Pole piece 86 has a lower central flow passage 86a, an upper flange with cylindrical flow passages 86b and a central upper bore 86c.
  • An annular flow sensing and by-pass module 88 has an active flow measuring section 89 (corresponding to members lla, llb Fig. 1) extending centrally or diametrically therethrough, and has an extension 88a including an outlet 88b which is held in bore 86c by O-ring 87a.
  • a closure plug 90 having O-rings 87b in its periphery is pressed into the housing top interior against spring 91 and a lock ring 92 inserted in interior ring groove 92a to hold the overall assembly.
  • Connector pins 93 extend through insulated feed-throughs in plug 90 and are connected by a flex cable to contact pads (Fig. 7) extending from the sensors in the flow measuring section 89.
  • Valve seat 83, armature 84, pole piece 85 and flow section module 88 are centrally located in the cylindrical housing 82 and each have outer side walls concentrically spaced from the interior side walls of the respective housing portions 82c, 82b and 82a so that an outer generally annular flow passage is formed to convey inlet gas to be measured in flow from inlet 94 up the outer annular flow passage and down through the sensing and by-pass module 89, 88, all as indicated by the shown flow arrows.
  • An armature coil 95 surrounds armature 84. Flow of current through the coil is in an amount dictated by a desired set point and by variations in flow sensed by the flow channel sensor and the bridge circuit (Fig. 1). Actuation of the coil moves the armature 84 so that a valve seal 96 on the axis and bottom of the armature is positioned above valve seat orifice 97 to regulate gas flow through the orifice.
  • Non-flat compression springs .85a, 85b center the armature and act to press the armature valve seal against orifice 97 so that upon cessation of current flow in the armature coil the valve returns to a fail-safe closed position.
  • passive by-pass channels 88 When the maximum flow required is in excess of the sensor's maximum flow rating, passive by-pass channels 88 are utilized. Their properties are chosen to match the sensor's pressure drop curve as a function of flow rate. The number of by-pass channels used determines the maximum flow rating of module 8 8 . The diameter of valve orifice 97 is chosen to allow the full required flow rate but not made so large as to limit control resolution.
  • the by-pass module envelope of the described preferred embodiment is a cylinder of 0.500 inches in internal diameter with the active flow sensor, bisecting the bypass conduit.
  • the active flow measuring section, 59 has a thickness of 0.049 inches.
  • the by-pass module has a length of 0.300 inches.
  • the passive by-pass channels are formed with 0.300 inch long cylindrical tubing segments of stainless steel having a 0.014 inch ID and 0.004 wall thickness grouped together to form a tube bundle.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Measuring Volume Flow (AREA)
EP19860200194 1985-04-10 1986-02-12 Débitmètre thermique de masse et régulateur Expired - Lifetime EP0203622B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US721535 1985-04-10
US06/721,535 US4685331A (en) 1985-04-10 1985-04-10 Thermal mass flowmeter and controller

Publications (3)

Publication Number Publication Date
EP0203622A2 true EP0203622A2 (fr) 1986-12-03
EP0203622A3 EP0203622A3 (en) 1987-04-22
EP0203622B1 EP0203622B1 (fr) 1990-09-05

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EP19860200194 Expired - Lifetime EP0203622B1 (fr) 1985-04-10 1986-02-12 Débitmètre thermique de masse et régulateur

Country Status (4)

Country Link
US (1) US4685331A (fr)
EP (1) EP0203622B1 (fr)
JP (1) JPH0765915B2 (fr)
DE (1) DE3673873D1 (fr)

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WO1992010726A1 (fr) * 1990-12-12 1992-06-25 University Of Cincinnati Micro-anemometre a semiconducteurs ameliore
US6631638B2 (en) 2001-01-30 2003-10-14 Rosemount Aerospace Inc. Fluid flow sensor

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Also Published As

Publication number Publication date
US4685331A (en) 1987-08-11
EP0203622B1 (fr) 1990-09-05
JPH0765915B2 (ja) 1995-07-19
JPS61235726A (ja) 1986-10-21
DE3673873D1 (de) 1990-10-11
EP0203622A3 (en) 1987-04-22

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